Based on the hypothesis that the genetic structure of the major histocompatibility complex (MHC) in chickens (B locus) parallels the H-2 complex in mice, objective 1 is to identify and characterize immune response (Ir) genes linked to the B complex. Objective 2 is to determine whether the B blood group system in chickens agrees with the 2-locus murine model and the HL-A complex in man. The key to our approach is the unique B1B1 genotype segregating in our S1 line which has consistently shown high adult mortality (4- to 4-fold higher than controls). The base population we have is line S1 (non-inbred) segregating for 3 B alleles: B1, B2 and B19. Also we have 7 inbred lines ranging up to 97% in coefficient of inbreeding. By introducing B1 into each inbred line followed by 3 or 4 backcrosses, we should produce nearly congenic or quasicongenic lines segregating within the B locus complex. The fact that the avian species has a clearly defined and easily separable dual immune system (B and T lymphocytes) argues for greater use of chickens in the study of immunobiology. Update: The principal accomplishment to date (6-30-80) under Objective 1 is that 4 haplotypes, including 2 parental and 2 recombinants, are now available in substantial numbers in our S1 Leghorn line. These involve the B region controlling SD and H effects and the Ir region controlling immune response which has made possible initial studies (in chickens) relating regions of the MHC to transplantation immunity, GVH, and to disease resistance. Additional studies are planned to determine whether the isoenzyme, glyoxalase 1 is linked to the B complex. Objective 2 depends on our finding a crossover haplotype involving Bx and By corresponding to the H-2K and H-2D regions in mice. A sizable breeding experiment, now underway will be coupled with new laboratory methods using the monoclonal antibody technic and immune fluorescence to detect Ia antibodies.